1. Field of the Invention
The present invention relates to a flame detecting device of a detector and a flame detecting method, in which generation of a fire is automatically detected making use of the physical phenomena (heat, smoke and flame) caused by a fire.
2. Description of the Related Art
Among conventional infrared ray type flame detection devices (hereinafter, referred to as xe2x80x9cflame detection devicexe2x80x9d), a flame detection device as illustrated in FIG. 8 is known as an example. In FIG. 8, 1 denotes a detection element, 2 denotes a frequency filter, 3 denotes a comparator, and 4 denotes an optical wavelength band pass filter. In practical applications, an amplifier, etc. for signal amplification is included, but omitted here for simplifying the description.
In the conventional flame detection device, the infrared ray energy in a monitoring area is converted into the electric signal by the detection element 1. The xe2x80x9cprescribed low frequency componentxe2x80x9d of the electric signal is taken out by the frequency filter 2. When the level of the low frequency component exceeds the reference level, the fire detection signal is outputted. The xe2x80x9cprescribed low frequency componentxe2x80x9d means the component including the frequency fc of the flicker (or shaking) of the infrared ray energy to be radiated from the flame, and fc is the extremely low frequency of several Hz or under.
FIG. 9 is a schematic view of how the flame burns. Generally speaking, the flame follows the growing process in which the flame is small immediately after the ignition, then, becomes gradually larger, and smaller as the combustible is exhausted, and is finally extinguished. However, when viewed in a short time, the size of the flame repeats the growth and deflation at a certain period. That is, as indicated in FIG. 9, the periodic fluctuation is repeated, wherein the burned-up flame takes in oxygen therearound and grows, while it becomes smaller for a moment once oxygen in its surrounding is reduced in amount, and then, grows again by the supply of oxygen from its outer side. It is proved that the repetitive cycle (the frequency fc) is characterized in that it is inversely proportional to the square root of the fire length for the combustible, e.g., liquid fuel. For example, the cycle is expressed by the following formula {circle around (1)} according to xe2x80x9cReport on Fire-fighting Research, Vol. 53, No. 24 (1982)xe2x80x9d (by Kunihiro Yamashita).
fc=k/{square root over ( )}L[Hz]xe2x80x83xe2x80x83{circle around (1)}
Where, k is a coefficient according to the kind of the fuel, and L is a value to express the quantity (fire length) of the fire. In general fire model, fc is e.g. about 2.5 Hz or 1.8 Hz. Thus, in a construction of FIG. 8, the xe2x80x9cflamexe2x80x9d caused by a fire can be detected if the passing frequency of a frequency filter 2 is 2.5 Hz, 1.8 Hz or each of these frequencies.
However, in the above-mentioned conventional flame detection device, the flame has been detected and judged based only on the level of the xe2x80x9cprescribed low frequency componentxe2x80x9d including the single frequency fc given by the formula {circle around (1)}. Thus, for the below-mentioned reasons, errors occur with a physical phenomenon which is not related to a fire, and thus there is a problem that of reliability of the conventional flame detectors is not sufficient.
FIG. 10a-c is a diagram to indicate the temporal fluctuation of the infrared ray energy, where (a) denotes a flame, (b) denotes a mercury lamp, and (c) is a rotary lamp. The flame is of course an object to be monitored because the flame detection device is used for detecting the flame, and in addition, the mercury lamp is often used for illumination of roads. The rotary lamp is often used in an emergency car as well as an alarm for an entrance or an exit of a parking lot or for road construction, and for a guide of a store. These mercury lamp and rotary lamp are examples of an infrared ray energy radiation body which are seen in a daily life.
FIG. 10 indicates the output of the infrared ray energy of the flame, the mercury lamp and the rotary lamp taken out through a chopper. In FIG. 10 (a) the infrared ray energy of the flame flickers at the frequency in the frequency band including the extremely low frequency fc, based on the above-mentioned reason. On the other hand, the infrared ray energy of the mercury lamp is maintained at the prescribed level (neglecting the fluctuation in power supply and noise) as indicated in FIG. 10 (b) and the frequency of the flicker is approximately 0 Hz (only DC part). Further, the infrared ray energy of the rotary lamp is clearly accompanied by, the periodic fluctuation as indicated in FIG. 10 (c) and its frequency is synchronous with the revolution of the rotary lamp. The rotary lamp is diversified in kind, including one. In which one lamp is turned in one direction at the prescribed speed (about two turns a second), and one in which a plurality of lamps are turned in a synchronous or asynchronous manner, and their frequency component is also diversified, but the rotary lamp of any kind is same in that it is periodically operated.
FIG. 11a-c shows an observation of the infrared ray energy of the flame, the mercury lamp and the rotary lamp (e.g., the output taken out as the temperature information through the chopper) relative to the frequency axis. Similar to FIG. 10, (a) denotes the flame, (b) denotes the mercury lamp, and (c) denotes the rotary lamp. The axis of abscissa means the frequency, and the origin means 0 Hz (DC part). The level in the vicinity of the origin is fairly large in (a), (b) and (c), and the peak is too high to be described in a graph, and omitted due to limitations of space.
Attention is paid to the flame in (a) and the mercury lamp in (b), and it is understood that their difference is quite obvious. That is, the flame has several levels in a frequency range 6 exceeding 0 Hz while the level in a similar frequency range 7 of the mercury lamp is approximately 0. Thus, the flame can be discriminated from the mercury lamp by comparing the level of the two using the frequency fc in the conventional technology.
However, in the rotary lamp in (c), similarity to the flame in (a) is high in that it has several levels in a frequency range 8 exceeding 0 Hz. When the level of the xe2x80x9cflamexe2x80x9d, the xe2x80x9cmercury lampxe2x80x9d and the xe2x80x9crotary lampxe2x80x9d is compared with each other using the frequency fc in the conventional technology, it has been difficult to clearly discriminate the flame from the rotary lamp though the flame can be discriminated from the mercury lamp, or the mercury lamp can be discriminated from the rotary lamp. This indicates that the fire detection signal can be mistakenly outputted if, for example, an emergency car having the rotary lamp approaches a place where a conventional flame detection device is installed. It thus means that there is a technological problem which must by solved by all means from the viewpoint of the reliability of a fire-fighting device or apparatus.
A flame detection device to solve the problem is also proposed. This device made use of not the phenomenon known as the CO2 resonance, but the radiation phenomenon that a peak appears in the vicinity of 4.4 xcexcm in the spectrum distribution of the infrared ray to be irradiated from an infrared ray radiation body accompanied by the flame. This flame detection device comprises, for example, a band pass filter for center extraction to pass the infrared ray of the wavelength around 4.4 xcexcm, and one or a plurality of band pass filters for periphery extraction to pass the infrared ray of the wavelength not including those close to 4.4 xcexcm so that these band pass filters can be switched by a switching mechanism such as a rotary plate. (Japanese Unexamined Patent Publication No. 50-2497, Japanese Unexamined Patent Publication No. 53-44937). Alternatively, the flame detection device comprises a detection element in which a band pass filter for center extraction is arranged on its forward side, and a detection element in which a band pass filter for peripheral extraction is arranged on its forward side.
These flame detection devices judge a fire when the differential intensity level between the infrared ray passing through the band pass filter for center extraction and the infrared ray passing through the band pass filter for peripheral extraction is not less than the prescribed value. However, even by these devices, it is still difficult to completely discriminate the flame from the rotary lamp though its discrimination accuracy is improved. Further, a band pass filter of narrow-band band pass filter is expensive, and when a plurality of band pass filters are provided, the price of the whole product becomes expensive, and still worse, there is a problem that the size of the product is increased. Still further, it is necessary to provide a switching mechanism, and a plurality of detection elements, and thus the price of the product and the size of the product are therefore markedly increased.
In the above-mentioned description, the xe2x80x9cmercury lampxe2x80x9d and the xe2x80x9crotary lampxe2x80x9d are illustrated as the infrared ray energy radiation body, but they are only representatives. That is, the xe2x80x9cmercury lampxe2x80x9d is a representative of the infrared ray energy radiation body free from the energy fluctuation, and the xe2x80x9crotary lampxe2x80x9d is a representative of the infrared ray energy radiation body whose period in energy fluctuation has the frequency component close to the frequency fc given by the above-mentioned formula {circle around (1)}.
Among others, U.S. Pat. No. 4,866,420 is given as a fire detection method using the flame flicker frequency spectrum. In the U.S. Pat. No. 4,866,420, a standardized idealized spectrum curve P(f) is compared with the real time spectrum for over 2 seconds. It is then judged whether or not the real time spectrum is deviated by more than the minimum quantity from the idealized spectrum curve P(f), or deviated from the prescribed window and the maximum deviation limit, and the detected signal is a true fire or a mistake. More specifically, as indicated in its flow chart of FIG. 6, it is judged that the detected signal is a true fire when all three limits (steps 34, 37 and 38) are judged to be Yes, while it is judged to be a mistake when any of the three limits are not complied with. In the first step 34, it is judged whether or not the standard deviation is smaller than 7.5 dB in order to roughly confirm a true fire. In the next step 37, it is judged whether or not the number of the curves or parts deviated from a window of 20 dB is smaller than the 25 Hz band width of 19%. In the final step 38, it is judged whether or not two maximum deviations are smaller than 25 dB. The steps 37, 38 are run in order to clearly confirm any mistake.
In the detection method of U.S. Pat. No. 4,866,420, a true fire is judged only when all three limits of the steps 34, 37 and 38 are cleared. Thus, there are problems that the detection method is complicated, and it takes a long time to detect a fire. In particular, the judgment of the step 37 is complicated and time-consuming because it must be judged whether or not the deviation is out of the 20 dB window at a plurality of points (24 points for 2 seconds).
Because the actual detection of a fire must be highly accurate and rapidly achieved taking into consideration the rescue of human lives, the detection method of U.S. Pat. No. 4,866,420 is difficult to apply to the detection of an actual fire and is not therefore a very practical detection method.
Accordingly, it is an object of the present invention to provide a flame detection device and a flame detection method which improve the identification performance of the flame from other infrared ray energy radiation bodies which are highly similar to the infrared ray energy fluctuation of the flame, and which improves the reliability of the fire-fighting equipment, and is thus more useful for society.
It is another object of the present invention to provide the flame detection device and the flame detection method capable of preventing the increase of the product price and the size of the device by detecting a fire with excellent reliability without increasing the number of band pass filters or detection elements.
It is still another object of the present invention to provide the flame detection device and the flame detection method suitable for the practical application by rapidly judging a fire.
In order to achieve the above-mentioned objects, the flame detection device of the present invention comprises a detection element to convert the infrared ray energy into the electric signal; a first extracting means to extract the signal of the first prescribed frequency range including the flicker frequency of the infrared ray energy of the flame from the output signal of said detection element; a second extracting means to extract the signal of the second prescribed frequency range including no flicker frequency of the infrared ray energy of the flame, but including the frequency on the higher frequency side than the first prescribed frequency range from the output signal of said detection element; and a judging means to judge whether or not a fire is generated based on the output signal of said first extracting means and the output signal of said second extracting means.
Also the flame detection method of the present invention comprising a first step to extract the signal of the first prescribed frequency range including no flicker frequency of the infrared ray energy of the flame and the signal of the second prescribed frequency range including no flicker frequency of the infrared ray energy of the flame, but including the frequency on the higher frequency side than that of said first prescribed frequency range from the output signal of the detection element to convert the infrared ray energy into the electric signal; and a second step to judge whether or not a fire is generated based on two signals extracted in said first step.
Because two frequency components are extracted from the output signal of the detection element, and a fire is judged based on these two frequency components, the present invention is advantageous in that the accuracy of the judgment can be improved compared with the judgment based on only the single frequency component used by conventional technology.
Further, provision of only one band pass filter and detection element each is sufficient, and a fire detection device can be constituted in an extremely simple manner when the signal is extracted to judge a fire by a micro processor. Thus, the increase in the product price and the size of the device can be prevented.
Still further, a fire can be judged in an extremely rapid manner because the fire is judged based on only first and second frequency components. That is, the judgment can be achieved in a short time because it is unnecessary to judge whether or not the deviation is out of the 20 dB window at a large number of points like the invention in U.S. Pat. No. 4,866,420. The fire detection device suitable for the actual fire detection can be constituted.
In the device of present invention, preferably, generation of a fire is judged when the signal extracted by said first extracting means has the level of not less than the first prescribed value in said judging means, and the signal extracted by said second extracting means does not have the level of not less than the second prescribed value. Or preferably, generation of a fire is judged when the ratio of the signal extracted by said first extracting means to the signal to be extracted by said second extracting means exceeds a third prescribed value.
In the method of present invention, preferably, generation of a fire is judged when the signal of the first prescribed frequency range extracted in said first step has the level of not less than the first prescribed value, and the signal of the second prescribed frequency range extracted in said first step does not have the level of not less than the second prescribed value in said second step. Or preferably, generation of a fire is judged when the ratio of the signal of the first prescribed frequency range extracted in said first step to the signal of the second prescribed frequency range exceeds the third prescribed value in said second step.
These judgments are advantageous in that, for example, the xe2x80x9crotary lampxe2x80x9d to show the trend of the fluctuation in the infrared ray energy similar to that of the flame, is not misidentified as the xe2x80x9cflamexe2x80x9d.
Further, in the device of present invention, preferably, said first extracting means and said second extracting means may analyze the frequency of the signal and extract the signal using a digital filter, a Fast Fourier Transformation method, or a maximum entropy method. Also, in the method of present invention, preferably, the frequency of the signal is analyzed and the signal is extracted using a digital filter, a Fast Fourier Transformation method or a maximum entropy method in said first step and said second step.
In this device and method, the present invention is advantageous in that the desired characteristic can be freely obtained at a low cost.
Still further, the fire can be judged more rapidly, and the flame can be more readily and accurately detected.
Still preferably, in the device and the method of present invention, said first prescribed frequency range is set up to include no DC part of the output signal of said detection element.
In this device and method, signal concerning infrared ray energy radiation body without fluctuation in infrared ray energy, for example, the xe2x80x9cmercury lampxe2x80x9d can be eliminated, thus fire detection is achieved easily and with certainty.
Still preferably, in the device and the method of present invention, said second prescribed frequency range includes at least multiple harmonic frequency of each frequency of said first prescribed frequency range.
In this device and method, frequency range which includes higher harmonic frequency of said first prescribed frequency range is set to said second range, artificial infrared ray energy radiation body with the fluctuation in the infrared ray energy, for example, the xe2x80x9crotary lampxe2x80x9d can be discriminated from that of an actual fire.
Still preferably, in the device and the method of present invention, said first prescribed frequency range is 0.5 Hz to 8.0 Hz, and said second prescribed frequency range is 8.5 Hz to 16.0 Hz. Or, preferably, said first prescribed frequency range is 0.25 Hz to 8.0 Hz, and said second prescribed frequency range is 8.25 Hz to 16.0 Hz.
These frequency ranges are theoretically and experimentally determined, and capable of most rapidly and correctly detecting a general flame.
Further, as described above, the device of present invention preferably comprises a detection element to convert the infrared ray energy into the electric signal; a first extracting means to extract the signal of a first prescribed frequency range of 0.5 Hz to 8.0 Hz including no DC part of said output signal but including the flicker frequency of the infrared ray energy of the flame from the output signal of said detection element by the Fast Fourier Transformation method; a second extracting means to extract the signal of a second prescribed frequency range of 8.5 Hz to 16.0 Hz including no flicker frequency of the infrared ray energy of the flame, but including the frequency on the higher frequency side than that of said first prescribed frequency range from the output signal of said detection element by the Fast Fourier Transformation method; and a judging means that a fire is generated when the signal extracted by said first extracting means has the level of not less than the first prescribed value, and the signal extracted by said second extracting means does not have the level of not less than the second prescribed value.
Also, as described above, the method of present invention preferably comprises a first step to extract the signal of a first prescribed frequency range of 0.5 Hz to 8.0 Hz including no DC part of the output signal but including the flicker frequency of the infrared ray energy of the flame and the signal of a second prescribed frequency range of 8.5 Hz to 16.0 Hz including no flicker frequency of the infrared ray energy of the flame but including the frequency on the higher frequency side than,that of said first prescribed frequency range from the output signal of a detection element to convert the infrared ray energy into the electric signal by the Fast Fourier Transformation method; and a second step to judge that a fire is generated when the signal of a first prescribed frequency range extracted in said first step has the level of not less than the first prescribed value, and the signal of the second prescribed frequency range extracted in said first step does not have the level of not less than the prescribed value.